A composite material can be defined as a macroscopic combination of two or more distinct materials, having a recognizable interface between them. Because composites are usually used for their structural properties, they often refer to materials that contain a reinforcement, such as fibers or particles, supported by a binder or matrix material. The discontinuous fibers or particles are generally stiffer and stronger than the continuous matrix phase, which can be a polymer, mastic, or hydraulic setting material, for example.
Fiber reinforced composites can be further divided into those containing discontinuous or continuous fibers. There is a tremendous potential advantage in strength-to-weight and stiffness-to-weight ratios of fiber reinforced composites over conventional materials. Their desirable properties can be obtained when the fibers are embedded in a matrix that binds them together, transfers the load to and between the fibers, and protects the fibers from environments and handling.
Glass fiber reinforced organic matrix composites are the most familiar and widely used, and have had extensive application in industrial, consumer, and military markets. Carbon fiber reinforced resin matrix composites are, by far, the most commonly applied advanced composites for a number of reasons. They offer extremely high specific properties, high quality materials that are readily available, reproducible material forms, increasing favorable cost projections, and comparative ease of manufacturing. Composites reinforced with aramid, other organics, and boron fibers, and with silicon-carbide, alumina, and other ceramic fibers, are also used.
Once continuous high strength fibers have been produced, they are usually converted into a form suitable for their intended composite application. The major finished forms are continuous roving, woven roving, fiberglass mat, chopped strand, and yarns for textile applications. Woven roving is produced by weaving fiberglass or carbon rovings, for example, into a fabric form. This yields a coarse product that may be used in many hand lay-up and panel molding processes to produce fiber reinforced plastics, mastics, roofing materials, and hydraulic setting boards. Many weave configurations are available, depending upon the requirements of the composite. Plain or twill weaves provide strength in both directions, while a unidirectionally stitched or knitted fabric provides strength primarily in one dimension. Many novel fabrics are currently available, including biaxial, double bias and triaxial weaves for special applications.
Fiber glass yarns are typically converted to fabric form by conventional weaving operations. Looms of various kinds are used in the industry, but the air-jet loom is the most popular. The major characteristics of a fabric include its style or weave pattern, fabric count, and the construction of warp yarns and fill yarns. Together, these characteristics determine fabric properties, such as drapability and performance in the final composite. The fabric count identifies the number of warp and fill yarns per inch. Warp yarns run parallel to the machine direction, and fill yarns are perpendicular.
Texturizing is a process in which the textile yarn is subject to an air-jet that impinges on its surface to make the yarn “fluffy”. The air-jet causes the surface filaments to break at random, giving the yarn a bulkier appearance. Carding is a process that makes staple fiber glass yarn from continuous yarn. Texturized or carded yarn absorbs much more resin or other matrix material, than unmodified yarn, and increases the resin-to-glass ratio in the final composite. Aramid and glass fibers are also known to be processed into needle-punched felts, which additionally, improves the resin absorption and/or fluffiness of the fabric.
While needling, texturizing, and carding have provided improved properties and more interesting dimensional characteristics for fabric, there remains a present need for manipulating yarns in a fabric to achieve even greater fabric thicknesses.